1. The Field of the Invention
The present invention relates to weighing systems for measuring the weight of a material carried on a conveyor. In particular, the present invention relates to systems for weighing material carried on a conveyor assembly, wherein the one or both of the pitch angle and the roll angle of the conveyor assembly is variable relative to the horizontal plane.
2. The Prior State of the Art
Conveyors are widely used in industry in order to transport material from one location to another. Conveyors are often used to transport material in manufacturing, construction, and agricultural applications, to name just a few. There are a wide variety of conveyors, including continuous belt devices that carry material and augers that move material using the rotary action of a helical member. Frequently, conveyors are used in processes wherein it is desirable not only to move the material but also to measure the weight of the material.
Over the years, a number of systems for measuring the weight of conveyed material have been developed. One approach involves discharging material from a conveyor onto a scale, whereby the weight of the material is measured. Frequently, it is inconvenient to discharge material onto a scale, since conveyors are often used to make material available at a desired location for uses that are incompatible with the scale. Another method involves positioning the entire conveyor assembly on the platform of a scale in order to measure the combined weight of the conveyor assembly and the material carried thereon. The tare weight of the conveyor assembly is subtracted from the combined weight measurement to determine the weight of the material. This method may significantly restrict the environments in which conveyor assemblies may be used, since the platform of the scale is cumbersome and prevents easy transport of the conveyor assembly. The size and cost of the equipment required in the foregoing methods further limit their practicability.
There have been developed further weighing systems which overcome some of the problems associated with the foregoing methods. For example, one system is based on the observation that the power required to operate a conveyor assembly is related to the weight of the material carried by the conveyor. Accordingly, the system involves monitoring the power consumption of the conveyor assembly and calculating the weight of the material from the measured data. In addition, there are systems that weigh material by using load cells under the conveyor belt or in the support member of the conveyor assembly.
Depending on the configuration of the conveyor assembly and the environment in which it is used, the systems that employ power consumption monitoring or load cells may adequately weigh the conveyed material without significantly interfering with the operation of the conveyor assembly. However, the foregoing systems generally are not suitable for measuring the weight of material on a conveyor having a variable pitch angle. For example, the power required to transport material is a function of the vertical distance through which the material is moved. Varying the pitch of a conveyor changes the power requirements of the conveyor assembly. Consequently, the power consumption of such a conveyor assembly does not uniquely correspond to the weight of the material. The method of monitoring power consumption has also been found to be limited to conveyors having a relatively shallow pitch, in a range from about five degrees above the horizontal to about five degrees below the horizontal. Likewise, the force measurements made by load cells in support members or under conveyor belts change as the pitch of the conveyor assembly changes. Accordingly, load cells have generally been useful only in conveyors that have a fixed pitch.
One approach for overcoming the problems of measuring weight on a conveyor having a variable pitch is presented in U.S. Pat. No. 4,788,930 to Matteau. The pitch of the conveyors taught by Matteau is variable in the sense that the angle between the centerline of the conveyor and the horizontal plane may be changed as desired. Accordingly, conveyors that are compatible with the weighing system of Matteau may have as many as one degree of rotational freedom relative to the horizontal plane. Matteau discloses using a clinometer in combination with a plurality of force sensors that detect the load on a segment of a conveyor belt. The clinometer provides information relating to the pitch of the conveyor, by which the force measurements from the force sensors may be adjusted in order to calculate the weight of the material.
The measurement system of Matteau, while overcoming some of the problems previously associated with measuring weight on a conveyor, has several drawbacks and limitations. For example, the system requires multiple sensors to be positioned under the conveyor belt, thereby increasing the complexity of the conveyor assembly. Moreover, Matteau extends to conveyors having at most one degree of rotational freedom relative to the horizontal plane. An example of such a conveyor assembly is one that is pivotally attached to a fixed base, such as a floor, and that may be pivotally raised and lowered by adjustment of a support member. Furthermore, many types of conveying chains and belts do not lend themselves to having weighing sensors positioned thereunder, regardless of the pitch of the conveyor.
There are a large number of conveyor assembly applications with which the existing weighing systems simply are not compatible. For example, conveyors are often transportable, and may be carried on a truck, harvesting equipment, or another vehicle. In such situations, it is common for the conveyor to be rotated relative to the horizontal plane with two degrees of freedom. In other words, both the pitch angle and the roll angle of such conveyors are freely variable.
Often such conveyors may be further varied by adjusting the support member. Thus, the pitch angle of such conveyors may change according to two mechanisms: unavoidable movement of the transporting vehicle and intentional adjustment of the support member. It can be understood that the angle of inclination with respect to the horizontal plane of such adjustable support members is only partially dependent on the pitch angle. Accordingly, a third independent variable, in addition to the pitch angle and the roll angle, is introduced into some conveyor/support member assemblies.
Examples of conveyor assembles that have variable pitch angles and roll angles are common in agricultural settings wherein crops are harvested using a harvesting vehicle equipped with a conveyor. There are also many other examples, including manufacturing and construction equipment for use with gravel, cement, other bulk materials, and the like. Conventional conveyor assemblies and previously existing weighing systems have not been able to accurately measure the weight of material carried on such variable-attitude conveyor assembles. Instead, costly and inconvenient alternatives have been used, such as weighing the material before or after being conveyed. Occasionally, the only available system has been to make unreliable estimates of the weight of the material flowing on the conveyor.
It can be understood that there is a need in the art for systems for weighing material carried by a conveyor having a variable pitch while avoiding the use of multiple load sensors as has been previously practiced. It would also be an advancement in the art to provide weighing systems that may be used with conveyor assemblies having more than one degree of rotational freedom relative to the horizontal plane, such as those that have variable pitch angles and roll angles. It would be particularly desirable to provide such weighing systems that could also be used with conveyors that are transported by trucks, harvesting equipment, or other vehicles.